In DwarfEHPrepare, after all passes are run, RewindFunction may be a dangling

pointer to a dead function. To make sure it's valid, doFinalization nullptrs
RewindFunction just like the constructor and so it will be found on next run.

llvm-svn: 217737

Author: yrnkrn

llvm/lib/CodeGen/DwarfEHPrepare.cpp

@@ -51,6 +51,11 @@ namespace {
 
     bool runOnFunction(Function &Fn) override;
 
+    bool doFinalization(Module &M) override {
+      RewindFunction = nullptr;
+      return false;
+    }
+
     void getAnalysisUsage(AnalysisUsage &AU) const override { }
 
     const char *getPassName() const override {